I'm trying something that I thought of to be simple 🙂 but somehow issn't to me.

I need to create new AD computer accounts based on the last account found in the AD.
In our company we have a strikt naming convention which should make it easy to create new accounts based on the last one.

Our naming schema is somehting like: USLAXDT123456

The last 6 digits are running numbers. So basically I only need to iterate this by 1.

My first approach would be to select -last 1 of the AD acccounts.
Split the name from the number. ($var = USLAXDT123456.remove(0,7)
Iterate the number... somehow maybe like this:
$var += 1

Think you're heading on the right lines. For splitting the number from the letters, you can also use .substring, and for working out the next number, Measure-Object with the -maximum parameter is your friend.